1. Field of the Invention
The present invention relates to a tracking servo method in an optical disk drive unit including a magnetooptic disk drive unit.
2. Description of the Related Art
In a general tracking servo method, a sum of respective amplitudes of reproducing signals is considered to be proportional to a tracking error signal. This tracking error signal is normalized by this sum to constantly hold a gain of the tracking error signal. However, there is a case in which this sum is not necessarily proportional to the tracking error signal. For example, when clock sample flags extend in the circumferential direction of an optical disk, their spatial frequencies in the circumferential direction of the optical disk are reduced so that the amplitudes of the reproducing signals are increased. However, the magnitude of the tracking error signal depends on the spatial frequencies of the clock sample flags on the optical disk in the radial direction thereof so that no magnitude of the tracking error signal is almost changed. The relation between the tracking error signal and the above sum is also changed by the shape and depth of pits forming the clock sample flags, or aberration characteristics of the light spot. Accordingly, a normalized tracking error signal is not necessarily constant at any time so that the gain of the tracking servo loop is changed.